First off, preserving the constitution and our very democracy is exactly what the democrats are attempting to do right now. Removing Trump from office would just be collateral to that.
That is where you are wrong, in fact. Sure, do the democrats completely dislike Trump and have they been on his case since before day 1, absolutely. Impeachment wasn't even an option for Pelosi, in fact she rallied against it UNTIL Trump finally crossed the line of what could be excused and what couldn't be. Impeachment wasn't even a reality until Trump pulled the Ukraine crap. Clinton, in all actuality shouldn't have been impeached for cheating on his wife and making a deposit into Lewinsky. At worst the guy was immoral/unethical but not worthy of impeachment. Trump on the other hand used the office of the president in an attempt for his own personal gain. That alone is a reason for impeachment and removal. Not even bringing in obstructing congress. If there was ever a valid time to use impeachment ever in our history it is now, against Trump.
The point of my original post was to state that despite what you might think of me I value the balance that we typically have between democrats and republicans. I'm afraid that in their effort to defend and protect Trump they actually do so much harm to their own party that it takes them forever to recover. Who knows, it may already be too late.